Drop in replacement for the native php file session handler with lock-timeout support. Work arround PHP Bug #72345.

FileSessionHandler.php

<?php

class FileSessionHandler implements SessionHandlerInterface
{
    /**
     * time in milliseconds how fast to poll the filesystem for a file-lock
     * in case it cannot be acquired / is (b)locked by other resources.
     *
     * @var int
     * @internal
     */
    const LOCK_POLL_INTERVAL = 30;

    private $savePath;
    private $fd;
    private $lockTimeout;

    /**
     * @param int $lockTimeout time in milliseconds how long the handler tries to acquire a file-lock
     */
    public function __construct($lockTimeout) {
        $this->lockTimeout = $lockTimeout;
    }

    public function open($savePath, $sessionName)
    {
        $this->savePath = $savePath;
        if (!is_dir($this->savePath)) {
            if (!@mkdir($this->savePath, 0770)) {
                throw new Exception('Unable to create session dir '.$this->savePath);
            }
        }

        return true;
    }

    public function close()
    {
        if (!$this->fd) return false;

        flock($fd, LOCK_UN | LOCK_NB);
        return fclose($this->fd);
    }

    public function read($id)
    {
        $this->fd = fopen("$this->savePath/sess_$id", "c+");
        if (!$this->fd) {
            throw new Exception("Unable to create session file $this->savePath/sess_$id");
        }

        $timeRemaining = $this->lockTimeout;
        $sleepMillis = self::LOCK_POLL_INTERVAL;
        while (!flock($this->fd, LOCK_EX | LOCK_NB)) {
            usleep($sleepMillis * 1000);
            $timeRemaining -= $sleepMillis;

            if ($timeRemaining <= 0) {
                fclose($this->fd);                
                throw new Exception('Unable to acquire session lock within '. $this->lockTimeout .'ms!');
            }
        }

        return (string)@stream_get_contents($this->fd);
    }

    public function write($id, $data)
    {
        if (!$this->fd) return false;

        rewind($this->fd);
        ftruncate($this->fd, 0);
        return fwrite($this->fd, $data) !== false;
    }

    public function destroy($id)
    {
        $file = "$this->savePath/sess_$id";
        if (file_exists($file)) {
            unlink($file);
        }

        return true;
    }

    public function gc($maxlifetime)
    {
        // we assume GC will be managed with different mechanics, e.g CRON
        return true;
    }
}